Wiki · Reference entry
Envelope
The set of conditions a system was approved to operate inside.
Which cases, which data, which volumes, which policies in force, for how long. An approval is never unconditional even when nobody writes the conditions down, so making the envelope explicit is mostly a matter of admitting what was already true. The useful part is that an explicit envelope can be checked, and can be noticed leaving.
Why it matters
You did not approve a system. You approved a system under conditions.